This disclosure relates to controlling the volume of ambient sound heard through headphones.
U.S. Pat. No. 8,798,283, the contents of which are hereby incorporated by reference, describes using two sets of filters in a active noise-reducing (ANR) headphone to either cancel ambient noise, or to admit ambient noise with a filter applied that counters the passive effects of the headphone, such that the user hears the ambient noise as if not wearing the headphones. That application defines such a feature as “active hear-through” with “ambient naturalness.”